A new confuciusornithid (Aves: Pygostylia) from the Early Cretaceous increases the morphological disparity of the Confuciusornithidae

摘要

Confuciusornithidae is the clade of Early Cretaceous birds most rich in materials and plays a central role in our understanding of the evolution of avian horny beaks and pygostyles. A handful of specimens demonstrate that this avian group is distinguishable from other basal birds by their robust, toothless upper and lower jaws, a fused scapulocoracoid and a tiny claw on the middle manual digit, among other features. Here, we report a new taxon of Confuciusornithidae, Yangavis confucii gen. et sp. nov., from the Early Cretaceous Jehol Biota, northeastern China. This new bird, however, has a normal-sized major digit claw, as in other basal birds, which was probably regained independently as Confuciusornithidae evolved, based on our phylogenetic study. Unfortunately, the biological significance of this trait is unclear owing to a lack of analogues in modern birds (manual claws are completely lost in adults). Yangavis confucii is differentiated from other confuciusornithids by its proportionally much longer forelimb. Our morphometric analysis indicates that the morphospace of Confuciusornithidae, with the addition of Y. confucii, is greatly broadened to a degree that it overlaps with the Early Cretaceous Ornithuromorpha and Enantiornithines, indicating that the biological diversity of confuciusornithids is greater than previously thought.